Ok - I can accept your answer in 8 minutes :) ...lol..really :) I just tried to and thats the response I got.
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GenadinikMar 31 '11 at 20:24

This is hideously annoying. I asked a question and got the right answer almost immediately. Why do I have to wait? Besides, you can always change the accepted answer later.
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marathonSep 25 '11 at 3:01

@marathon I've seen a few cases where people had accepted answers straight-away, thinking that they got the right answer, but which turned out to be incorrect (or of fairly low quality). Sometimes the asker doesn't have the expertise to tell whether an answer just sounds right or is actually right. Other answers can come later from more expert users. Very few technical questions can be asked, answered and tested (just to check it works) within 5 minutes or so. I think it's actually better practice to wait longer (1 or 2 days) to give a chance for others to provide answers too.
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BrunoJul 25 '12 at 18:42

My friend and I have accounts on Stack Overflow. We make an agreement to increase each others' rep and get badges by answering each others' questions. So we try to ask and answer as many questions as possible, as fast as possible.

By limiting how soon an answer can be accepted, the system prevents us from artificially boosting our rep too quickly.

Disclaimer:

Hopefully it goes without saying that this is just a hypothetical, I have never done this nor have any plans to do so.